150 



STUDIES IN ADVANCED PHYSIOLOGY. 



tissue ill question, and after losing some of its substance 

 into the lymph, it is returned by means of the veins to the 

 right auricle as impure blood, and from the right auricle 

 proceeds to the right ventricle, which was its starting 

 point. It will thus be seen that in one complete circula- 

 tion the blood passes through the heart twice, and passes 

 through at least two sets of capillaries, those of the lung 

 and the systemic capillaries. It has already been stated 

 that this proceeds with such rapidity that the time required 

 for such a complete circulation is but little more than half 

 a minute. 



THE HEART. 



1. Position. The energy to keep this entire current 

 moving is furnished by the heart, which is a large, muscular 

 organ situated in the chest extending from about the second 

 to the fifth ribs. While it varies in size under varying cir- 

 cumstances its average size may be roughly indicated by 

 comparing it with the double fists of the person. It is 

 placed diagonally in the chest, with the apex extended 



Fig. 70. DIAGRAM TO SHOW RELATIVE POSITION OF HEART IN THE CHEST. 



towards the left side striking the chest wall in front, about 

 between the fifth and sixth ribs, while the base extends 



